Signal comparison-based location determining method

ABSTRACT

At least one portable RF communications device in conjunction with at least two fixed-location service-area antenna stations respectively capable of RF communication with the at least one device performs the steps of: (I) using a portable device at a selected location to measure RF communications signals from the plurality of local fixed-location service-area antenna stations and electronically storing at least two of the respective reception signal strength measurements; and (II) monitoring a portable device location by causing the device to measure reception signal strength associated with local fixed-location service-area antenna stations signals, and to electronically compare these measurements with the stored at least two measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/533,238,filed on Sep. 19, 2006 now U.S. Pat. No. 7,706,811 and entitled “SignalComparison-Based Location Determining Method”. The disclosures of saidapplication and its entire file wrapper (included all prior artreferences cited therewith) are hereby specifically incorporated hereinby reference in their entirety as if set forth fully herein.Furthermore, a portion of the disclosure of this patent documentcontains material which is subject to copyright protection. Thecopyright owner has no objection to the facsimile reproduction by anyoneof the patent document or the patent disclosure, as it appears in thePatent and Trademark Office patent file or records, but otherwisereserves all copyright rights whatsoever.

TECHNICAL FIELD

The present invention generally relates to methods for determining thelocation of a mobile telephone, or of a mobile communications device.More specifically, the present invention relates to a method fordetermining the location of a mobile telephone, wherein the mobiletelephone is preferably capable of performing measurements of signalcharacteristics deriving from signals being received from mobiletelephone service area antennas, of performing calculations relatedthereto, and of storing these measurements and/or calculation results.

BACKGROUND ART

Simply stated, there is a longstanding problem of providing highaccuracy location data for mobile devices, such as mobile telephones. Inthe most critical aspect, the problem is to maintain user privacy ofprecise location data of the mobile telephone user. Nevertheless, therealso remains a need in the art for simple straightforward improvementsin determining the precise location of mobile devices; especially inpoor signal-reception locations such as in dense multi-story urbancenters. Furthermore, there is a need in the art for providing anelevation component to location data, so as to locate a device in amulti-story structure.

Motorola, Inc., Overview of 2G LCS Technologies and Standards (3GPP TSGSA2 LCS Workshop LCS-010019—London, UK, 11-12 Jan. 2001)—discusses whylocating mobile phones becomes a hot topic in telecommunicationsindustry, and what technologies are being studied and standardized.

Y. Zhao, “Mobile Phone Location Determination and Its Impact onIntelligent Transportation Systems,” IEEE Transactions on IntelligentTransportation Systems, vol. 1, no. 1, pp. 55-64, March 2000. —providesmore information on different location technologies and related locationservices.

There are many location-determining methods used to determine thelocation of a cell phone. These methods differ in the level of accuracythey provide as well as their implementation. In general these methodscould be divided into methods that involve the cellular networkparticipation and those that don't (handset based only).

Methods that involve the cellular network participation include:

-   Cell-ID-   TDOA—Time Difference Of Arrival-   TOA—Time Of Arrival-   AOA—Angel Of Arrival-   EOTD—Enhanced Observed Time Difference-   A-FLT—Advanced Forward Link Trilateration-   A-GPS—Assisted GPS (Global Positioning System)

Methods that rely solely on the handset to determine its position:

-   GPS—Global Positioning System

Expect Cell-ID where the location of the handset is simply determined tobe within the area of the cell, where the cell's base station locationis known and the accuracy depends on the size of the cell (accuracy ofanywhere between 100 meter and 3,000 meters) all other methods requiredifferent levels of calculations either by the network or the handset orboth.

A substantially similar field where virtually the same class of locationbased need arise is in the area of ubiquitous computing. Essentially,with respect to location based applications, the primary differencebetween the mobile telephony and ubiquitous computing relates toprivacy—since the mobile telephone user might prefer not to allow hislocation to be monitored, while privacy is a non-issue for a ubiquitouscomputer attached to a box in a large warehouse or to a piece of luggagein an airport customs clearance center or to a semi-assembled componentin a multifaceted manufacturing facility or to a semiautonomous vehiclein a recreation center, etc.

A Survey and Taxonomy of Location Systems for Ubiquitous Computing—byJeffrey Hightower and Gaetano Borriello (Technical Report UW-CSE01-08-03)—“Emerging mobile computing applications often need to knowwhere things are physically located. To meet this need, many differentlocation systems and technologies have been developed. In this paper wepresent the basic techniques used for location-sensing, describe ataxonomy of location systems, present a survey of research andcommercial location systems that define the field, show how the taxonomycan be used to evaluate location-sensing systems, and offer suggestionsfor future research. It is our hope that this paper is a usefulreference for researchers and location-aware application builders alikefor understanding and evaluating the many options in this domain.”

SpotON: An Indoor 3D Location Sensing Technology Based on RF SignalStrength—by Jeffrey Hightower and Gaetano Borriello—(UW CSE TechnicalReport #2000-02-02) “Providing a reliable technology and architecturefor determining the location of real world objects and people willundoubtedly enable applications, customization, and inference notcurrently possible. This paper documents the creation of SpotON, a newtagging technology for three dimensional location sensing based on radiosignal strength analysis. Although there are many aspects to the topicof location sensing and several of them will be briefly discussed, thispaper is primarily concerned with the hardware and embedded systemdevelopment of such a system.”

For many mobile telephone location based services, constant calculationof a user's handset location is required. For example, if a user askedto receive food coupons whenever he enters a specific area or to beinformed if a child carrying a cell phone left a certain perimeteraround the house, or if the user asked for a group call to his cellphone and home phone every time that he is at home; in order to give himthe option to answer calls to his cell phone on his landline.

From a network perspective, in an anticipated emerging world whereLocation Based Services (LBS) are expected to be widely used and ofthose services many require constant monitoring of a user's cell phonelocation, those methods will require the networks to have a lot ofinfrastructure dedicated to the determination of handsets' locations.

From a privacy perspective, having the cellular network constantlymonitor a user's location is problematic to many people. For example,the user asked to receive coupons for merchandise on sale when he is inthe shopping area next to his home. However, that same user is troubledby a prospect that, in order for the coupons to be sent, the user'slocation must be constantly monitored so as to find out when he entersthe shopping area.

Obviously the privacy problem could be solved by having the cell phoneitself monitor its position, and activate an application when the cellphone concludes that the user has entered the shopping area, etc. Thisclass of solution is also amenable for adaptation to ubiquitouscomputing situations—since it simply makes the location monitoring logicpart of a distributed computing architecture.

Having the cell phone monitor its position will also significantlyreduce the infrastructure required by the cellular network to determinethe location of handsets. This is also true in ubiquitous computingapplications.

Currently a cell phone can determine its geographical location by usinga GPS receiver. The challenges with using a GPS in a handset—is that GPSrequire significant calculations that takes time, up to several minutes;it is difficult to get GPS signals in dense urban areas; and GPS doesnot distinguish between different elevations at the same location. Thus,in our shopping area example, GPS would not distinguish between enteringa large department store from entering a shopping center plaza in afloor below or entering a professional service office in a floor above.

A-GPS (Assisted-GPS), which is intended to reduce the time it takes todetermine a location as well as possibly calculate the location in thenetwork in order to reduce the complexity required from the cell phone,once again requires the network.

Using Cell-ID by the cell phone is limited as a cell area locationresolution is not good enough for most location based applications. Onthe ubiquitous computing side, division of large areas into micro-cellspresents a substantially similar location accuracy threshold.

There are, of course, numerous patents that have contributed to progressin this art—especially in the field of cellular telephones—mostespecially since there is an ongoing attempt to reach compliance withregulations calling for instant automatic location reporting forcellular telephone users requesting emergency services (police,ambulance, fire department, etc.).

U.S. Pat. No. 7,057,556—Method And Apparatus For Geolocating A WirelessCommunications Device—“The time difference of arrival for a signalreceived at two or more receiving sites as transmitted from a wirelesscommunications device, is determined by a frequency domain technique.The constituent frequencies of the signals received at the two or morereceiving sites are determined, including the phase, or a valuerepresentative of the phase, of each frequency component. The phasevalues for the same frequency are subtracted to yield a phase differencevalues as a function of frequency. The slope of the function representsthe time difference of arrival for the wireless communications devicesignal as received at the two receiving sites. To determine the mobilelocation based on the determined time difference of arrival values, aseed or initial location is first assumed for the wirelesscommunications device and the distance difference of arrival (the timedifference of arrival multiplied by the speed of light) is calculated.The calculated time difference of arrival is then used to adjust thedistance difference of arrival by continuously iterating the position ofthe wireless communications device until the calculated distance ofarrival and the calculated time difference of arrival (as multiplied bythe speed of light) are within a predetermined margin.”

U.S. Pat. No. 7,050,786—Method And Apparatus For Locating A WirelessDevice—“Disclosed is a method and apparatus for locating a wirelessdevice especially useful for locating a cellular telephone making a callfrom an unknown location. The call may be a request for emergencyassistance, or for location-based commercial services, for example.Various embodiments may optionally include a mobile location component,a cellular telephone enabled to chirp-on-demand, and/or aninterferometer link. A mobile location component may include adirectional antenna. The directional antenna may be mounted on anantenna boom on top of an emergency vehicle, for example. The mobilelocation component may alternately or additionally comprise a hand-heldunit. System elements may cooperate to generate a situation awarenessmap or other display. The mobile location component may be moved in thegeneral direction of a first location calculation associated with afirst circular error of probability. After being moved in the generaldirection, the mobile location component may cooperate with otherelements to determine a second location calculation associated with asecond circular error of probability. Second and subsequent locationcalculations are of increasing precision, enabling an emergency vehicleor attendant to zero in on a cellular telephone.”

U.S. Pat. No. 6,972,717—Method And Apparatus For Enhanced 911 LocationUsing Power Control In A Wireless System—“A method of locating a mobiletelephone includes steps of receiving, transmitting, increasing anddetermining. In the receiving step, a first base station receives a callfrom a mobile telephone, the call including a dialed number and a TDMAsignal. In the transmitting step, the base station transmits a controlmessage to the mobile telephone when the dialed number meets apredetermined criterion, such as being 911. The control messageinstructs the mobile telephone to transmit the TDMA signal at a maximumpower. In the increasing step, the mobile telephone increases the TDMAsignal to maximum power in response to the control message. Then in thedetermining step, location information for the mobile telephone isdetermined based on at least one characteristic of the TDMA signalreceived at-least one of the first base station and other base stations.In an alternate embodiment, the method is practiced in a mobiletelephone and the power level is automatically increased in response tothe dialed number meeting a predetermined criterion.”

U.S. Pat. No. 6,674,403—Position Detection And Location Tracking In AWireless Network—“A system and method for performing real-time positiondetection and motion tracking of mobile communications devices movingabout in a defined space comprised of a plurality of locales isprovided. A plurality of access points are disposed about the space toprovide an interface between mobile devices and a network havingfunctionality and data available or accessible there-from. Knowledge ofadjacency of locales may be used to better determine the location of themobile device as it transitions between locales and feedback may beprovided to monitor the status and configuration of the access points.”

EP 1241909—Method And Computer Readable Medium For A Program ForLocation Determination Of A Mobile Terminal—“A method for locationdetermination of a mobile terminal by means of radio connections whichare controlled by a common server, characterized by providing a leastone pair of different radio zones closely spaced from each other so thatdistinct directional information transversely to a boundary between thepair of radio zones is provided upon recording of the movement of themobile terminal in the zones. Furthermore, preferably characterized inthat a pair of radio zones comprises a first zone and a second zone, andthat information is stored in the server defining that the mobile unitis present on one side of said boundary if the mobile unit is firstrecorded in the second zone and then in the first zone, and definingthat the mobile unit is present on the other side of said boundary ifthe mobile unit is first recorded in the first zone and then in thesecond zone.”

The challenges, therefore, are to develop a location-determining methodthat would: (A) Take place on the cell phone for the benefit of privacy(monitoring of user location by the cell phone and not by the cellularnetwork) as well as in order to reduce the infrastructure required bythe cellular network to determine cell phone locations; (B) Will notrequire heavy calculations by the cell phone in order to be able todetermine a location fast and with minimal resources so the method besuitable for cheap handsets and not only expensive handsets withcapabilities to perform heavy calculations; and (C) Provide accurateenough location determination.

Simply stated, there is a need for performing geographical locationdeterminations with ordinary RF communications hardware (without GPScapability) because that is less expensive than performing the samedetermination with GPS hardware components. Furthermore, there isanother independent need to perform location determinations within ascope of privacy to the user—in order for him to permit applicationevents that depend on location. There is also a need for locationdetermination in locations where GPS reception is problematic. Inaddition, there is a need for determining elevation components oflocation without the addition of additional hardware—especially fordevices that are already GPS capable. Likewise, for both cellulartelephony and the ubiquitous computing arts there is a need to provideelevation location data and/or to reduce infrastructure intensiveapplication for location determination, progress in at least one ofthese areas would constitute a meaningful contribution to alleviating alongstanding need in the art; and would set the stage for the progressof further location-knowledge-dependent applications.

DISCLOSURE OF INVENTION

The aforesaid longstanding needs are significantly addressed byembodiments of the present invention, which specifically relates to aSignal-Comparison Based Location-Determining Method. The instant methodis especially useful in telecommunications and/or ubiquitous computingapplications wherein there exists a need to provide improved privacy,and/or to provide elevation location data, and/or to reduceinfrastructure intensive application for location determination.

The instant invention relates to embodiments of a Signal-ComparisonBased Location-Determining Method, operable by at least one portable RFcommunications device in conjunction with at least two fixed-locationservice-area antenna stations respectively capable of RF communicationwith the at least one device wherein the stations are substantiallycontinuously operating, and the method is comprising the steps of:

-   (A) Registering a selected location by first-causing a portable RF    communications device at the selected location (i) to receive an RF    communications signal from a plurality of local fixed-location    service-area antenna stations, and (ii) to measure reception signal    strength respectively associated with the received signal from at    least two of the plurality of antenna stations;-   (B) Recording the selected location by electronically storing at    least two of the respective reception signal strength measurements;-   (C) Monitoring by second-causing a portable RF communications    device (i) to receive communications signals from a plurality of    respectively local fixed-location service-area antenna stations,    and (ii) to measure reception signal strength associated with the    signals; and-   (D) Determining if the portable RF communications device of the    Monitoring step is at the selected location of the registering step    by electronically comparing measurements in the monitoring step with    the stored at least two measurements of the Recording step.

According to a simpler categorization, the instant invention relates toa methodological embodiment (see FIG. 1) whereby at least one portableRF communications device in conjunction with at least two fixed-locationservice-area antenna stations respectively capable of RF communicationwith the at least one device perform the steps of: -100-(I) using aportable device at a selected location to measure RF communicationssignals from the plurality of local fixed-location service-area antennastations and electronically storing at least two of the respectivereception signal strength measurements; and -110-(II) Monitoring aportable device location by causing the device to measure receptionsignal strength associated with local fixed-location service-areaantenna stations signals, and to electronically compare thesemeasurements with the stored at least two measurements.

Please note, the present invention is herein described with a certaindegree of particularity, however those versed in the art will readilyappreciate that various modifications and alterations may be carried outwithout departing from either the spirit or scope, as hereinafterclaimed. For example, the majority of the description relates to directmeasurements of signal strengths and direct comparisons of thosemeasurements. Such direct measurements are generally correct in acellular telephone GSM environment, however in a cellular telephone CDMAenvironment it is the relative signal strengths that form an importantmetric for comparative purposes. Similarly, for other antenna spaceenvironments, measurements and comparisons thereof should conform to theunderlying policy that governs the management of antenna space signalstrength management—or of equivalent antenna space transmission metriccharacteristics. For example, a strongest signal may be used as a unitto help normalize other simultaneous measurements; however, since thatstrongest signal may encounter inoperative events or radicalenvironmental changes (e.g. construction of a signal blocking structurebetween the “strong” antenna and the reception location), one wouldprefer to retain a capability to renormalize measurements within thecontext of the instant method.

Simply stated, a conceptually instant enabling embodiment of the presentinvention is a cellular telephone device that looks at the signalstrengths (and preferably corresponding local base station service areaantenna IDs) to characterize an antenna space signal-reception signatureas being substantially equivalent to a current location. The deviceneeds a means for remembering this signal strength (preferably with theantennas' IDs), and this means may be on the device per se, kept at aremote storage (or even transferred from the current device to theowner's next cell phone). The device can “know” that it has returned tothe original location where the signal strengths were measured (and theantennas' IDs preferably captured). Since the device is capable ofreceiving and measuring such signals, the device simply performs suchreception measurements and compares these measurements with theremembered signal strength combinations. Whenever there is a substantialequivalence between the remembered signal strengths (and IDs) and thecurrently being monitored signal strengths (and IDs), then the devicecan conclude that it is probably at the original location where theoriginal measurements were performed.

Now, illustrative enabling embodiments of a Signal-Comparison BasedLocation-Determining Method of the instant invention—according to asimplified aspect—substantially relate to a method for determining acell phone (or a ubiquitous computer) location comprising: (A) at adesired location—Causing a cell phone (or a ubiquitous computer) tomeasure signal strengths from surrounding cells and to record the signalstrengths measured by the cell phone (or the ubiquitous computer) fromthe surrounding cells; (B) at a current location—Causing a cell phone(or a ubiquitous computer) to measure the signal strengths fromsurrounding cells; and (C) Causing the Cell phone (or ubiquitouscomputer) to compare the measured signal strengths from surroundingcells at the current location with the recorded signal strengths fromsurrounding cells at the desired location in order to determine whetherthe cell phone or the ubiquitous computer of the present location isalso at the desired location.

Today, given our technological orientations, one's normal concept oflocation combines some small number of quantitative coordinatesaccording to some consistent coordinate system. Typically location isdescribed by a Cartesian intersection of latitude and longitude; andsometimes including elevation too. Elsewhere, location is described bytriangulation from two known positions. Nevertheless, when desiring toexpress the location of a mobile telephone (i.e. cellular telephone,“tell phone”, pager, area wide wireless telecommunications apparatus,blackberry, ubiquitous computer, or the likes), the ability to captureprecise longitude, latitude, or angular measurements become calculationintensive—well beyond the economic value of their engineering precision;most particularly if these calculations must be performed on the mobiletelephone.

Now, the instant invention takes note of an additional ergonomicparameter, typical of mobile telephones, which greatly simplifies thesecalculations; perhaps even increasing the accuracy of the resultantlocation specification. Let's start with a simplest example; a mobiletelephone is in the possession of a resident of a small house, which isin a sparsely populated rural environment. By the very nature of thissituation, that small house probably only falls within the antennacoverage of a single cellular telephone service providing antenna.Accordingly, if the cell-phone captures a distance equivalentmeasurement between itself (when located in that small house) and thearea service antenna, then one would expect that this measurement simplydescribes a constant radius distance around the service antenna.Accordingly, from a strict scientific perspective, whenever thecell-phone measures that it is at that radius distance from the serviceantenna, it can only logically presume that the probability of it alsobeing in that small house is substantially proportional to the fragmentof arc that the house represents with respect to the circumferencespecified by that radius.

OK, now if the owner of the cell-phone is a tractor driver who typicallycontinuously drives back and forth across the length and breadth of theservice antenna coverage area, then the presumed probability that thecell-phone radius measurement corresponds to him being in that house isas described. However, if he is in that house an average of eight hoursper day, then there is already a high probability that the radiusmeasurement from the cell-phone indicates that he is in the house. Morelikely, the cell-phone owner is not an indentured round-the-clocktractor driver, but an ordinary vehicle commuter who goes from thathouse to various other locations, using established paved roads. Thisbeing the case, there are perhaps four to six locations where theseroads coincide with that radius measurement, and it is only of minimalprobability that a part of one of those roads follows that circumferencefor any span or that the cell-phone owner parks his vehicle at such alocation. Accordingly, there is an already very high probability thatthe radius measurement from the cell-phone indicates that he is in thehouse.

One can easily provide a significant increase in this already very highprobability by delaying confirmation of the measurement calculation—atleast until it is performed at least twice. Specifically, to eliminatespurious observation of the cell-phone owner traversing at thatcircumference, one need only wait to see that the same measurement hadbeen made twice with perhaps a 2-3 minute interval wait there-between.That interval would be enough to edit out occurrence of the cell-phoneowner stopping or driving over (or along) the circumference; or stoppingat some incidentally located traffic light, etc.

Moving on to a slightly more realistic scenario, the house is located ina rural environment (see FIG. 2) where there are occasional clusters ofbuildings and three service antennas -200- -210- -220- such that thereis a 40% probability of a building being in the coverage area of asingle service antenna, a 40% probability of a building being in theoverlapping coverage area of two service antennas, and a 20% probabilityof a building being in the overlapping coverage area of three serviceantennas. In this instance, the cell-phone captures respective distanceequivalent measurement(s) between itself (when located in that smallhouse) and each of area service antenna(s). In order to make thisexample more simplistic, one can say that the cell-phone ignores anydistance equivalent measurement (e.g. service antenna signal strength asmeasured at the mobile device, arrival times or phases of signalsarriving from surrounding cells, or the likes) below a predeterminedthreshold. Now in this example, there is yet a substantially higherprobability that a confluence of the captured radius measurement(s) fromthe cell-phone indicate that he is in the house.

However, instead of the simplistic assumption, that we only considerdistance equivalent measures for service antenna signals that arecapable of providing a reasonable quality of service to the mobiletelephone unit, we substitute a more realistic assumption—specificallythat we consider distance equivalent measures from service antennasignals that are discretely recognizable (i.e. where the service antennaID is non-ambiguously recognizable with the signal that the mobiletelephone receives from the respective antenna). Now, for almost everyrural, suburban, and urban location where there is mobile telephoneservice provided—the mobile telephone will be able to equate its currentposition with a unique coordinate signature comprising at least one (butpreferably a plurality of) identifiable service antennas and theirrespective distance equivalent measurement there-from, as appreciatedfrom their respective signal strengths (or like metrics).

Simply stated, if a mobile telephone (at a user selected location)measures a plurality of service antenna signals and stores these withtheir respective service antenna identifications, then that mobiletelephone (or an equivalent unit) upon observing an identical list ofservice antennas with substantially identical respective signalstrengths—can reasonably conclude that it is within a predeterminedproximity of the original user selected location. We will call thecoordinate of the user selected location a “fingerprint”—because webelieve that each such location has (associated with it) a substantiallyunique combination of service antenna identifications with respectivedistance equivalent measurements (e.g. service antenna signal strengthas measured at the mobile device, arrival times or phases of signalsarriving from surrounding cells as measured by the mobile device, or thelikes).

For practical purposes, the fingerprint should carry substantially aboutthe same probability of ambiguity between all combinations of tworegion-similar physical locations (having the “same” fingerprint) as theGlobal Positioning System (GPS). Recall that GPS has a nominalprobability of giving biased reading (false reading)—especially in thelocations near where GPS will give no reading whatsoever—such as insidebuilding or in dense urban areas or in steep mountain gorges, etc.Specifically, GPS will fail to give a proper coordinate reading wheneverit can not simultaneously locate three positioning satellites. However,under a different (but similarly improbable combination ofcircumstances), the fingerprint concept of the instant invention mayfail to provide adequate location recognition (ambiguity). Our firstorder suspicion is that the fingerprint concept will be at least as good(over a large collection of urban, suburban, and semi-rural settings) asthe GPS system—albeit the fingerprint location concept does not requirethe special hardware of GPS Systems (antenna & computation hardware).Accordingly, for an equal quality of service, it is reasonable tosuggest that the fingerprint concept embodiments will always be lesscostly than equivalent GPS embodiments.

These respective distance equivalent measurements are generally notadequate for direct triangulation calculation from the known positionsof the service antennas—because in mountainous regions and moreparticularly in urban landscapes, the signal strength is a function ofthe convolutions of the signal path length and of the absorption orreflection of materials encountered there-between. Nevertheless, sinceservice providers generally measure ground truth to locate shadow spotsand the likes, the accumulation of GPS coordinates in association withlocation fingerprints—will eventually create adequate computationalclosure for the provision of transformations between fingerprints andstandard geographical map coordinates—via an intermediate fingerprint“terrain” map database.

Intentionally, cell phones including both a GPS and the instantinvention method could help build such a database. The GPS would be usedto identify a desired location for the first time and the signalstrength fingerprint will be used to recognize the desired location fromthat point in time and onwards). In a practical application, this meansthat a mobile telephone calling an emergency number (police, fire,ambulance, etc.) and transmitting the fingerprint that it currentlyrecords—should thereby provide the emergency response with adequateinformation to transform the fingerprint into a real world location andto arrive at same. Thus, until there is substantially complete closurein the construction of “fingerprint” topological database maps, afingerprint supplemented GPS reporting to emergency services wouldprovide a best opportunity embodiment for those services to locate thecaller.

Furthermore, because service antennas are generally not located atidentical elevations (nor coplanar); and the elevation of serviceantennas is known, Thus, measuring at two locations, having identicallatitude and longitude but differing in elevation, will not yieldidentical fingerprints. This is a significant advancement over GPS,which is generally elevation insensitive for location determination(i.e. differentiating between floors of a multi-story building, shoppingcenter, or the likes).

Now, according to more heuristic variant embodiments of the instantinvention, the mobile telephone will generally measure and record agreater than necessary plurality of service antenna identifiers withtheir respective distance equivalent metrics. Thereafter, when themobile telephone monitors its respective present location in servicearea antenna signal strength space (or the likes), then finding acorrelation with a majority of such measurements in a single record willlead the device to logically conclude that there is a high probabilitythat this is the location of that measurement—albeit that there isperhaps a new building between the current location and one or more ofthe proximate service area antennas. Accordingly, the device may buildup an evolving description to characterize a known location. Similarly,the device may normalize the measurements in each record or develop pairwise combinations of relationships between measurements of a singlerecord—thereby opening the variation embodiment wherein a differentmobile telephone may use this same data; which in turn allows the userof this mobile telephone to transfer his collection of records toanother device that may not identically measure service antennacharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, embodiments including the preferred embodiment will nowbe described, by way of non-limiting example only, with reference to theaccompanying drawings. Furthermore, a more complete understanding of thepresent invention and the advantages thereof may be acquired byreferring to the following description in consideration of theaccompanying drawings, in which like reference numbers indicate likefeatures, and in which an embodiment “name” is only for purposes ofhelping a reader to differentiate between embodiments and among variousgroups of aspects and/or variations therein, and wherein:

FIG. 1 illustrates a schematic view of a “methodological” embodiment;

FIG. 2 illustrates a schematic view of an antenna space reception map

FIG. 3 illustrates a schematic view of a “basic” embodiment;

FIG. 4 illustrates a schematic view of a “first appurtenance” embodiment

FIG. 5 illustrates a schematic view of a “second appurtenance”embodiment;

FIG. 6 illustrates a schematic view of a “system” embodiment;

FIG. 7 illustrates a schematic view of an “illustrative enabling”embodiment

MODES FOR CARRYING OUT THE INVENTION

Embodiments and aspects of the instant invention may be embodied invarious forms, wherein a Basic embodiment (see FIG. 3) of the instantinvention relates to A Signal-Comparison Based Location-DeterminingMethod, operable by at least one portable RF communications device inconjunction with at least two fixed-location service-area antennastations respectively capable of RF communication with the at least onedevice wherein the stations are substantially continuously operating,and the method is comprising the steps of: (A) Registering -300- aselected location by first-causing a portable RF communications deviceat the selected location (i) to receive an RF communications signal froma plurality of local fixed-location service-area antenna stations, and(ii) to measure reception signal strength respectively associated withthe received signal from at least two of the plurality of antennastations; (B) Recording -310- the selected location by electronicallystoring at least two of the respective reception signal strengthmeasurements; (C) Monitoring -320- by second-causing a portable RFcommunications device (i) to receive communications signals from aplurality of respectively local fixed-location service-area antennastations, and (ii) to measure reception signal strength associated withthe signals,; and (D) Determining -330- if the portable RFcommunications device of the Monitoring step is at the selected locationof the registering step by electronically comparing measurements in themonitoring step with the stored at least two measurements of theRecording step.

Now in greater detail, the Basic instant embodiment is operable by atleast one portable RF communications device in conjunction with at leasttwo fixed-location service-area antenna stations respectively capable ofRF communication with the at least one device wherein the stations aresubstantially continuously operating. As is likewise mentioned elsewhereherein, the RF device may be a cellular telephone or a communicationsenabled ubiquitous computer or any mobile device capable (I) ofreceiving RF signals and (II) of measuring their respective signalstrengths (or of measuring any parameter that is equivalent to signalstrength), and of communication (internal or external) with a modulethat can store data and can logically and mathematically compare valuesand therewith arrive at a comparative conclusion between two sets ofdata. Essentially these sets of data are those created in the storingstep and in the monitoring step. Depending on the sophistication ofsoftware enabling the comparative conclusion, the operations involvedmay be simply logical comparisons, arithmetically threshold (rounded)logical comparisons, arithmetic, probabilistic, fuzzy logic, neuralnetwork enabled, heuristic, or the likes.

Furthermore, in greater detail, we now turn our attention to the Basicinstant embodiment step of: (A) Registering a selected location byfirst-causing a portable RF communications device at the selectedlocation (i) to receive an RF communications signal from a plurality oflocal fixed-location service-area antenna stations, and (ii) to measurereception signal strength respectively associated with the receivedsignal from at least two of the plurality of antenna stations. This is adata collection step where the portable device comes to measure theantenna signal space reception characteristics at the selected location.Depending on the sophistication of the specification enablement, oneshould give priority of “attention” to the strongest signals—since theseare probably the most robust for characterizing the antenna spacereception signature of this selected location. A highly sophisticatedenablement will collect lots of measurement data and then be able tocome to viable conclusions using which ever verifiable fraction of thatdata is reproducible at a subsequent instantiation. A more simplisticapproach would be to just take the up to five strongest signals.

Likewise, in greater detail, we now turn our attention to the Basicinstant embodiment step of: (B) Recording the selected location byelectronically storing at least two of the respective reception signalstrength measurements. Storage may be on the device per se ortransferred to a remote storage facility. Privacy for a cellulartelephone user preferred that the data be stored on the cellulartelephone unit, however for other types of device or where privacy isnot important (e.g. monitoring luggage or logistics of components in awarehouse or police in the field or the likes) the data may be offloaded. The offloading may be done in real time or may be done in batchat convenient intervals or to testify to the location of the device at atime in question or the likes.

In addition, in greater detail, we now turn our attention to the Basicinstant embodiment step of: (C) Monitoring by second-causing a portableRF communications device (i) to receive communications signals from aplurality of respectively local fixed-location service-area antennastations, and (ii) to measure reception signal strength associated withthe signals. Essentially, this step is by first approximation alike intechnical detail to the Registering step. However, the monitoring stepmay be of a different degree of detail to the registering step. Forexample, the registering step may collect lots of data while themonitoring step collects sparse first order data, and then collects morecomprehensive data for the next step (Determining). Essentially, onedoes not want to dedicate lots of portable device resources to themonitoring activity, so one may divide the monitoring into low accuracymonitoring activities—which just tell the device if there might beanything to seriously compare (such as the surrounding antennas' IDs atthe selected location and current location are the same and thereforemore resources should be allocated to the monitoring); and higheraccuracy monitoring activity—which takes the necessary resources to makethe necessary determining definitive.

Finally, in greater detail, we now turn our attention to the Basicinstant embodiment step of: (D) Determining if the portable RFcommunications device of the Monitoring step is at the selected locationof the registering step by electronically comparing measurements in themonitoring step with the stored at least two measurements of theRecording step. Where privacy is of concern then all of the four stepsshould be performed on a single mobile device. However, in a privacyirrelevant shared data environment, one might even reach the case whereRegistering is done on a first device, Monitoring is done on a seconddevice, Storing is done in an offsite facility, and Determining is donein a different offsite facility.

According to a first implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Registeringstep includes identifying at least one ID within at least one of therespectively received signals; and the Recording step includes storingeach of the at least one IDs with the respective reception signalstrength measurement. In the context of this first implementationaspect, it is according to a preferred manifestation that the Monitoringstep includes identifying at least one ID within at least one of therespectively received signals and the Determining step includeselectronically matching at least one ID of the Monitoring step with thestored at least one ID of the Recording step. Simply stated, while themethod may be accomplished without having an ID on every signal, havingsuch an ID would make the job of concluding, that the current locationis the selected location, much easier. Nevertheless, since ID is notrequired, then have one or more signals with ID may also provide forlogic simplification. In the case of cellular telephony, the ID seems toalways be available in service areas. However, in areas plagued byintermittent service problems, sometimes a device will see a signalwhere the ID is not recognizable. In other applications, the device isnot a cellular telephone but does use the cellular base station signalsas “landmarks” for registering “location”—so the device might not havethe ability to look for an ID even if the ID is clearly visible on therespective signals.

According to a second implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Monitoringstep includes iteratively performing the sub-steps C.i and C.ii with apredetermined time delay between successive iterations of C.i such thatthe monitoring step data is used only if a substantial portion of thesuccessive C.ii measurements are alike within a predeterminedthreshold—since this indicates that the portable RF device of step C istemporally immobile. This returns to our case above, where a driverhappens to stop at a traffic light that just resembles a knownconfluence of signal strengths. However, if the driver does not staythere more than a minute or two, we would conclude that he has notreally arrived at the selected location.

According to a third implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Determiningstep includes improving the electronically stored at least two of therespective reception signal strength measurements of step B by storingat least one measurement of step C therewith—thereby upgradingrobustness of the electronically stored measurements. This case relatesto creating an ability to improve the correctness of the basic method.For example, in the urban terrain, new building are being built and oldones are being modified while streets are being paved with alternatematerials, large billboards are being erected, old antennas are replacedand new ones are added—all of which cause the preferred method toattempt to upgrade the data of the original registering step; and tolearn new aspects of the current antenna space environment. Anotherrealistic example is the addition of a cell site and its impact onpre-existing cells.

According to a fourth implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Registeringstep includes accessing a GPS location coordinate for the selectedlocation and Recording step includes keeping the GPS location coordinatewith the stored signal strength measurements. This aspect anticipatesthat a transformational data bank could be created by collectingcorrespondences between GPS (latitude longitude) coordinates and antennaspace reception “coordinates” for the same location. If sufficientcorrespondence data is collected, then a never registered location canbe found by grabbing antenna space reception “coordinates” andextrapolating them within the correspondence set. This would be of greatbenefit for “911” emergency service location-determining compliance;since locations failing to be able to report GPS could be known fromextrapolation using only the reception signature.

According to a fifth implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Registeringstep includes directly transferring the measurements within the portableRF communications device to a storage module therein whereat theRecording step is preformed. By contradistinction, according to a sixthimplementation aspect of the Basic embodiment of the Signal-ComparisonBased Location-Determining Method, the Registering step includes, via RFcommunications, transferring the measurements from the portable RFcommunications device to a storage device whereat the Recording step ispreformed; and wherein the Recording step includes, via RFcommunications, receiving the measurements. Please note that these fifthand sixth aspects are not necessarily mutually exclusive since onboardstorage on the device improves response time while offsite storagecomplements creation of a database of such reception space signatures.

According to a seventh implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method the Registeringstep allows a user to append a designation tag to the registrationdata—for example—denoting the data to be stored as “Home” or “Office” or“222 East Street” or the likes.

According to an eighth implementation aspect of the Basic embodiment ofthe Signal-Comparison Based Location-Determining Method, the Determiningstep includes calculating a confidence metric according to a degree ofcorrelation between the measurements in the Monitoring step with thestored at least two measurements of the recording step. This complementsour discussion of evolving signal strength reception characteristics ofthe urban landscape; and also complements the detail of the preamblethat any specific service area antenna may be taken out of service forrepairs, upgrades, and the likes. Thus, it is preferred to introducestatistical comparisons, threshold values, heuristics, and the likes toimprove a user's confidence in the accuracy of the determining stepresult.

Further embodiments and aspects of the instant invention may be embodiedin various forms, wherein a first appurtenance embodiment (see FIG. 4)of the instant invention relates to A Signal-Comparison BasedLocation-Determining Database recorded on a tangible memory media -400-and having recorded thereon signal-strength location correlation dataderiving from the Registering step or the Monitoring step of theSignal-Comparison Based Location-Determining Method, the Basicembodiment of the Signal-Comparison Based Location-Determining Method,and to any combination of its eight aforementioned aspects.

Now, additional embodiments and aspects of the instant invention may beembodied in various forms, wherein a second appurtenance embodiment (seeFIG. 5) of the instant invention relates to An article of manufactureincluding a computer usable medium having computer readable program codeembodied therein for Signal-Comparison Based Location-Determining, thecomputer readable program code in said article of manufacture including:(AA) first computer readable program code -500- for causing a computerto Register a selected location by first-causing a portable RFcommunications device at the selected location (i) to receive an RFcommunications signal from a plurality of local fixed-locationservice-area antenna stations, and (ii) to measure reception signalstrength respectively associated with the received signal from at leasttwo of the plurality of antenna stations; (BB) tied to the firstcomputer readable software, second computer readable program code -510-for causing the computer to Record the selected location byelectronically storing at least two of the respective reception signalstrength measurements; (CC) tied to the second computer readablesoftware, third computer readable program code -520- for causing thecomputer to Monitor by second-causing a portable RF communicationsdevice (i) to receive communications signals from a plurality ofrespectively local fixed-location service-area antenna stations, and(ii) to measure reception signal strength associated with the signals;and (DD) tied to the third computer readable software, fourth computerreadable program code -530- for causing the computer Determine if theportable RF communications device of the Monitoring step is at theselected location of the registering step by electronically comparingmeasurements in the monitoring step with the stored at least twomeasurements of the Recording step; and

Finally, please note that embodiments and aspects of the instantinvention may be embodied in various forms, wherein a particularlygeneralized embodiment of the instant invention relates to ASignal-Comparison Based Location-Determining system (see FIG. 6),substantially as herein before described and illustrated, andcharacterized by using interconnected software enabled modules on atleast one portable RF communications device, said modules operating inconjunction with at least two fixed-location service-area antennastations that are respectively capable of RF communication with the atleast one device wherein the stations are substantially continuouslyoperating, and these software modules include: (A) a registration module-600- for Registering a selected location by first-causing a portable RFcommunications device at the selected location (i) to receive an RFcommunications signal from a plurality of local fixed-locationservice-area antenna stations, and (ii) to measure reception signalstrength respectively associated with the received signal from at leasttwo of the plurality of antenna stations; (B) a recording module -610-for Recording the selected location by electronically storing at leasttwo of the respective reception signal strength measurements; (C) amonitoring module -620- for Monitoring by second-causing a portable RFcommunications device (i) to receive communications signals from aplurality of respectively local fixed-location service-area antennastations, and (ii) to measure reception signal strength associated withthe signals; and (D) a determination module -630- for Determining if theportable RF communications device of the Monitoring step is at theselected location of the registering step by electronically comparingmeasurements in the monitoring step with the stored at least twomeasurements of the Recording step.

For the sake of good order, it is noted that the reader is now directedto recall: the aforementioned illustrative enabling embodiment (see FIG.7) of Signal-Comparison Based Location-Determining Method—according to asimplified aspect—substantially relate to a method for determining acell phone (or a ubiquitous computer) location comprising: (A) at adesired location—Causing -700- a cell phone (or a ubiquitous computer)to measure signal strengths from surrounding cells and to record thesignal strengths measured by the cell phone (or the ubiquitous computer)from the surrounding cells; (B) at a current location—Causing -710- acell phone (or a ubiquitous computer) to measure the signal strengthsfrom surrounding cells; and (C) Causing -720- the Cell phone (orubiquitous computer) to compare the measured signal strengths fromsurrounding cells at the current location with the recorded signalstrengths from surrounding cells at the desired location (in order todetermine whether the cell phone or the ubiquitous computer of thepresent location is also at the desired location).

According to a first variation of the illustrative enabling embodiment,measuring signal strength includes identifying a unique ID in a portionof the signal.

According to a second variation of the illustrative enabling embodiment,the current location cell phone measuring the signal strengths fromsurrounding cells is done at regular time intervals or at scheduledtimes or a predetermined following an event or following a request.

According to a third variation of the illustrative enabling embodiment,the comparing step (C) includes comparing measured signal strengths on acell by cell basis (for example, according to the unique ID of the firstvariation or according to other signal characteristics that facilitatedifferentiation). Preferably, two signal strengths measured by the cellphone from the same cell at the current location and the desiredlocation are considered to be similar if their respective difference iswithin a predetermined threshold. Alternatively, signal strengthsmeasured at a single location are compared to one-another so thatspurious changes of RF absorbing or RF reflecting materials in thesurrounding geographical region can be accounted for and intelligentlyignored—as for example will be the case if an area of dirt roadsre-paved with asphalt or one of asphalt re-paved over with brick-work,etc. Now, according to a further improvement, the compared signalstrengths measured by the cell phone at the current location and at thedesired location are considered similar when at-least a pre-determinednumber of these measurements (and preferably but not necessarily withtheir respective IDs) are matched—thereby resulting in a determinativejudgment that the cell phone has returned to the desired location. Itshould be noted that there is a very low probability that a cell phone(measuring a few different signal strengths at the desired location)will at some future moment be in a different location having that samecombination of signal strengths. Thus, the method of the instantinvention may be accomplished without resorting to ID identification orcomparison—however, presumably a larger number of no-ID signals would beprobabilistically necessary to be measured and conclusively matched fromthe desired and current locations. According to a more preferred form ofthis variation embodiment, the at-least pre-determined number of “thesemeasurements” of cells are those cells with have the strongest measuredsignals. By way of a supplementary metric, the sum of the differencesbetween measured signal strengths from the same cells at the currentlocation and at the desired location, being less than a pre-determinedthreshold, will result in a determination that the cell phone hasreturned to the desired location.

According to a fourth variation of the illustrative enabling embodiment,measuring signal strength includes measuring an equivalent signal aspectcharacteristic such as the cell phone measuring arrival times or phasesof signals arriving from surrounding cells or the likes.

According to a fifth variation of the illustrative enabling embodiment,the comparing step (C) includes the calculating of relations betweensignals of cells; especially but not necessarily wherein the cells areneighboring cells. Preferably, this is wherein cells are consideredneighboring cells if their signals are the strongest signals measured bythe cell phone. Substantially this means the most proximate basestations antennas are substantially respectively neighbors toone-another.

Thus, the combination of measured signal strengths from surroundingcells (including possibly more distant than just “surrounding” cells'service area antennas) as measured by the cell phone at a certainlocation creates a unique fingerprint identifying the location.

This unique fingerprint, which unlike GPS signals is always available tothe cell phone, can be used to determine that a cell phone has returnedto a location it has already been to.

Now we will turn our attention to discuss other useful aspects of theembodiments of the instant invention. Since the instant invention isused to determine that a cell phone current location is the same as alocation that the cell phone has already been to in the past, there isno need to translate the combination of measured signal strengths atsurrounding cells to geographical coordinates. Simply stated, for thesimply purposes of the cell phone, substantially matching a currentantenna space reception fingerprint (or a significant portion thereof)with a predetermined antenna space reception fingerprint (or asignificant portion thereof) constitutes a return to an indeterminatecoordinate space “brigin”—and this “Substantial matching” is sufficientto accomplish the most basic objectives of the instant invention.

The combination of signal strengths measured by the cell phone fromsurrounding cells at a specific location provides an accurate definitionof the location with many advantages over existing locationdetermination methods: [0092]1) No need to calculate geographicalcoordinates, which significantly reduces the amount of requiredcalculation. [0093]2) Signal strengths can always be measured by a cellphone without the assistance of a cellular network. [0094]3) The simplecalculation required to compare the signal strengths measured by a cellphone from surrounding cells at a current location and a desiredlocation makes this method ideal for any cell phone in general and cheapcell phones that do not have a GPS and do not have the capability forsignificant calculation specifically.

The apparent disadvantage of the instant invention method is that itrequires the cell phone to record the signal strengths at a desiredlocation. Thus according to simplest embodiments of the instantinvention, the user can not ask for a location based service by simplyentering an address or a geographical coordinates. Having said that,many location based services are initiated when a user is at thelocation where he would like to receive the service, and therefore thesuggested method's disadvantage does not limit the user for theseservices.

Moreover, the simple embodiment instant invention method can be used inconjunction with other location-determining methods. If geographicalcoordinates are initially used for the definition of a location basedservice, as soon as the cell phone is determined to be present at thosegeographical coordinates regardless of whether the cell phone determinedits geographic location (using a GPS or another method) or the cellularnetwork determines the geographic location of the cell phone or acombination, the cell phone can record the signal strengths at thatgeographical location and going forward instead of determining the cellphone has returned to that location by checking the geographicalcoordinates use the suggested invention as it requires less resourcesand is faster.

Accuracy-wise, the more cells a cell phone can measure the signal itreceives from them, the more accurate the instant method is.Nevertheless, as described in the probabilistic considerations of the“small house” example (above), a large plurality of reception fromdifferent base station antennas is not necessarily required to provide“adequate” location identity confirmation (returning to a predeterminedmeasured location). When it is described according embodiments of theinstant invention that a cell phone measures a signal-strength from asurrounding cell, it means that the cell phone measures the strength ofthe signal sent by that cell's base station antenna. These measurementsare from the perspective of the location of the reception device (thecellular telephone, ubiquitous computer, etc.) and substantially form ainstance of an antenna space reception fingerprint; even though asignificant portion thereof is sufficient for many applications.Clearly, as a cell phone user moves around he gets closer to some cellsand get further away from other cells, which is reflected in thecombination of signal strengths measured by the cell phone from thesurrounding cells (generally speaking, the closer a cell phone is to acell's base station the stronger the signal it will measure from thecell's base station). Exceptions, to the basic physics approximation ofsignal strength as proportional to a square of the distance separatingthe cell phone from the base station antenna, are created by thereflectivity and absorbance characteristics of materials in and alongthe signal path(s) there-between.

Unlike other location-determining methods, as it is the cell phone thatmeasures the signal strengths, obstacles that impact the accuracy andavailability of other location-determining methods do not impact thesuggested method. Such obstacles include the non-availability of GPSsignals within buildings or accuracy problems originating from thepropagation of signals to cell towers and their measurement by systemslocated at the cell towers.

Here follows another non-limiting implementation—

The user reaches a location where he would like a certain location basedservice to take place every time he reaches that location.

Such a service could be having calls to his cell phone ringsimultaneously both on his cell phone and the landline at the desiredlocation every time he is determined to be at the desired location (theuser's home for example) by the software responsible of determining itslocation which is running on the cell phone (a geo-location based groupcalling service).

An example of another service will be to receive discount coupons frommall stores every time the user enters the shopping mall next to hishome (the shopping mall is a desired location).

The user will stand in the location where he would like something totake place every time he reaches that place (a desired location). Usinghis cell phone he will choose the action that he wants to take place.The action he would like to take place will then be associated with thelocation where the user is standing where the location will be definedby software running on the cell phone as the combination of signalstrengths measured by the cell phone from surrounding cells.

It should be noted that the surrounding cells would each be uniquelyidentified by the cell phone.

A cell might be identified by a cell phone by the same unique ID used bya cellular network to identify the cell (assuming the cell phone hasaccess to the full ID) or possibly by a combination of the cell ID asrecognized by the cell phone along with an LAC (Location Area Code).Obviously the cell phone may use other variables it receives fromsurrounding cells base stations to uniquely identify a cell by eitherusing one variable or a combination of variables.

The cell phone may further use the cellular network it self as one ofthe variables identifying a cell in order to avoid a case where twodifferent cellular networks the cell phone is roaming between use thesame IDs (as recorded by the cell phone) to identify their cells.

It should further be noted that even if cell IDs used by a cell phonewill not be unique per cell (i.e. two or more cells in a cellularnetwork will have the same ID as recorded by the cell phone), the oddsof the cell phone recognizing two different locations as the samelocation are very low since it will require the same cell IDs to be usedin two different areas and the same signal strengths to be recorded fromthe ‘same’ cells in two different locations.

Once the cell phone records the signal strengths measured by the cellphone from surrounding cells at a desired location, the combination ofthe recorded signal strengths from surrounding cells are used as thecoordinates of the desired location.

It should be noted that there is no limit on the number of desiredlocations that could be recorded and tracked by the cell phone.

After the cell phone records the desired location coordinates (thecombination of signal strengths from surrounding cells), the cell phonewill check its location as reflected by the signal strengths fromsurrounding cells at specific time intervals (every 2 minutes forexample) or at specific times (every 5 minutes during the day and every15 minutes between 3 am and 6 am) or depending on the rate the user'slocation changes (if the user does not change its location for more than60 minutes then the rate of checking the location can be reduced fromevery 5 minutes to every 20 minutes to save battery power) or at theoccurrence of an event (such as the cell phone switching the basestation it is registered with) or upon a request from the network to doso or upon a request from an application to do so or upon a request fromthe user to do so etc.

If the current location's surrounding cell IDs are different from thedesired location's surrounding cell IDs then the cell phone does notneed to continue the comparison, the current location is clearly not thedesired location.

When the signal strengths from the cells surrounding the currentlocation are identical to the signal strengths measured by the cellphone from the exact same cells (same cell IDs) at the desired locationthen the cell phone is determined to have returned to the desiredlocation (i.e. current location=desired location) and the location basedapplication which is pending the return of the cell phone to the desiredlocation will be activated.

Having said that, when comparing the current location with the desiredlocation, depending on the location based application, a threshold couldbe defined based on how close the current location should be to thedesired location in order to activate the desired application.

The threshold could be a number that if the difference between twosignal strengths measured by the cell phone from the same cell at thecurrent location and the desired location is less than that number themeasured signal strengths from the specific cell at the current locationand the desired location would be considered similar.

If the difference between the measured signal strength at the currentlocation and the measured signal strength from the same cell at thedesired location for each of the surrounding cells is less than thethreshold then the cell phone's current position will be considered thesame as the desired location or within reasonable range and the locationbased application which is pending the return of the cell phone to thedesired location or to its area will be activated.

In another implementation, it could further be defined that it is enoughthat the difference between the measured signal strength at the currentlocation and the measured signal strength from the same cell at thedesired location for at-least a pre-determined number of surroundingcells (3 cells for example) will be less than the threshold for thecurrent location to be considered within reasonable range from thedesired location and as a result to activate the location basedapplication which its activation is pending the return of the cell phoneto the area of the desired location.

In another implementation, it could further be defined that the at-leastpre-determined number of cells described in the previous paragraph arethose cells with the strongest measured signals.

It should be mentioned that while the more the signal strengths frommore surrounding cells are taken into account, the more accurate thelocation determination is, a possible implementation might take intoaccount as little as one signal strength (the strongest one) in order todetermine whether the cell phone has returned to the area of the desiredlocation.

In a different implementation, if the sum of the differences betweenmeasured signal strengths from the same cells at the current locationand desired location is less than a pre-determined threshold then itwill result in determining that the cell phone has returned to thedesired location or the desired location area.

It is worthwhile to analyze the suggested method in a typical GSMimplementation and a typical CDMA implementation.

In a typical GSM system, GMSK modulation is used on the BCCH (BroadcastControl Channel) carrier. The BCCH carrier is continuously transmittedand without variation of RF level. Cell phones measure the receivedsignal level from surrounding cells by tuning and listening to theirBCCH carriers. The measured signal strengths (levels) are used forhandover purposes.

The suggested location-determining method is therefore ideal for GSMwhere surrounding cells BCCH carriers transmit at the same RF level atall times.

In a typical CDMA system such as a DS-CDMA (Direct Sequence CDMA), sinceall signals in a DS-CDMA system are sharing the same bandwidth andoverlapping in time, the power levels of the signals transmitted by thecell phones (uplink) as well as the power level of the signalstransmitted by the base station (downlink) are controlled to achieveacceptable signal-to-interference ratio (SIR) for all users (sometimeit's also called C/I—Carrier to Interference ratio). Controlling the SIRhelps maximize the system capacity by minimizing the probability for acall to be dropped due to a too low SIR.

While different algorithms for calculating downlink power allocation(i.e. the signal levels/strengths transmitted by a CDMA base station)exist, typically what's common to those different algorithms is thestriving to achieve a minimal reasonable SIR for all cell phonesconnected to the base station where the noise component of the SIR ateach of the cell phones is assumed to mainly be impacted by the signalstransmitted by surrounding cells. Additionally, the sum of all signalstransmitted by a base station to cell phones registered with the basestation can not exceed the maximum power the base station transmitter iscapable of.

The lower the signals transmitted by surrounding cells' base stationsthe better the reception at a cell's cell phones. Downlink power controlaims to reduce the amount of interference in neighboring cells byadjusting the power of each cell's base station transmitter.

Substantially, this outlines an iterative process where the signalstrengths transmitted by base stations of neighboring cells arecorrelated.

The question then, how would the location determination method describedhere handle measured signal strengths of surrounding cells that vary asa function of cell phone traffic in a CDMA system?

One way could be to have the cell phone record signal strengths at adesired location at different times of day at different days of the weeksince cell phone traffic at cells is known to have a repetitive pattern.For example, on Monday between 12 pm and 2 pm people will use their cellphone to make and receive calls at a specific cell in approximately thesame way as they will use their cell phones on the following Mondaysbetween 12 pm and 2 pm, which means that the downlink transmitted powerby this cell and the neighboring cells will be approximately the same onMonday between 12 pm and 2 pm as well as on the following Mondaysbetween 12 pm and 2 pm since the downlink power is a function of cellphone traffic and the downlink transmitted power of neighboring cells iscorrelated.

Having said that, ideally a user will identify a desired location to thecell phone only once at one point in time and will not need to repeatthe identification of the desired location in different times.

Taking into account the correlation of downlink transmitted signals ofneighboring cells, by calculating the relations between the measuredsignal strengths of neighboring cells, a cell phone can identify that itreturned to a desired location by comparing the calculated relationsbetween neighboring cells at current location with the calculatedrelations between neighboring cells at the desired location. Since thecorrelation between downlink transmitted signals by cells' base stationsis among neighboring cells and a cell phone will not know which of themeasured signals belong to neighboring cells and which tonon-neighboring cells, in one suggested implementation the cell phonecan assume that the cells transmitting the strongest signals are thecells closest to the cell phone and therefore neighboring cells. Thecell phone will therefore take into account only the signal strengths ofthe cells transmitting the strongest signals as those cells will beassumed neighboring cells by the cell phone, therefore their signalscorrelated and therefore the relations between those cells' signals willrepresent the cell phone's location. The number of cells assumedneighboring cells could vary depending on factors such as total numberof signal strengths measured by the cell phone that could indicatewhether the cell phone is in an urban area or in a rural area or ameasured signal strength exceeding a threshold calculated by dividing ameasured signal strength by the strongest measured signal at the currentlocation etc.

An example of the above suggested implementation will be—a location isidentified to the cell phone as a desired location by the cell phoneowner.

The cell phone measures the signal strengths of surrounding cells. Thecell phone measures 10 signals from 10 surrounding cells. The cell phonechooses the 4 cells with the strongest signals as neighboring cells(cells #1, 4, 6, 9). The cell phone calculates the ratio between thechosen 4 signals by dividing the 3 less strong signals by the strongestsignal (assuming that cell #4 has the strongest signal). The cell phonerecords the 3 relations (cell #1 signal/cell #4 signal, cell #6signal/cell #4 signal and cell #9 signal/cell #4 signal). The cell phonemay further record the measured signal strengths of the 4 chosen cells.From that point in time onward, the cell phone checks to see if signalsfrom unique cells #1, 4, 6 and 9 can be measured by the cell phone. Ifthe cell phone can measure signals from cells #1, 4, 6 and 9, the cellphone calculates the relations between cells #1, 6 and 9 to cell #4. Ifthe calculated relations at the current location are identical to therecorded relations the cell phone determines that it has returned to thedesired location. The cell phone can determine that it has returned tothe desired location or to an area close enough to be considered thedesired location by subtracting each of the relations at the currentlocation from each of the corresponding relations at the desiredlocation and demanding that the each of the subtraction for each of therelations does not exceed a certain threshold or that the sum of thesubtractions does not exceed a certain threshold or alternatively anyother formula.

The above example assumes that one cell (cell #4 in the above example)will always have the strongest signal at the desired location (while thesignal of cell #4 will vary as a function of number of subscribers atneighboring cells the assumption is it will always be relatively thestrongest). This assumption will not be true in the case the cell phoneis located at equal distances to the base stations of 2 cells' basestations—cell #4 and cell #1. The cell phone might be registered withcell #4 at 2 pm on Monday when the number of subscribers at cell #1 isvery high and the number of subscribers at cell #4 is low but at 7 pmthe same day when the number of subscribers at cell #1 will be low andthe number of subscribers at cell #4 will be very high the cell phonewill be registered with cell #1 at the same physical location.Accordingly, if the cell phone would have measured the signal strengthsat 2 pm and 7 pm cell #4 signal would have come stronger only at 2 pmwhile at 7 pm the signal of cell #1 would have come stronger. Wetherefore need to accommodate this case in the location determinationalgorithm when used in a CDMA system or other systems with the samecharacteristics. When a cell phone is on the border of 2 cells, thesignals as measured by the cell phone will be close to each other. Inone possible implementation the algorithm can allow a higher threshold(which will make relations not as close when subtracted still less thanthe threshold that was made higher). In another possible implementationthe cell phone can divide the signal strength of the chosen cells not bythe signal of the strongest cell but by the sum of the signals of the 2strongest cells if the two strongest cells are close enough in strength.For example, if at 2 pm the signal strength of cell #4 is only slightlystronger than the signal strength of cell #1, the cell phone willcalculate the following relations: [0135]cell #6 signal/(cell #4signal+cell #1 signal) [0136]cell #9 signal/(cell #4 signal+cell #1signal)

Obviously, the above are just suggested implementations and otherpossible implementations using other formulas are possible.

It was mentioned that more measurements taken at the desired location atdifferent points in time could help improve the location determination.It was further mentioned that the user will ideally identify a locationas a desired location to a cell phone only once. Since in many cases adesired location is a user's home or office and after the identificationof a location as a desired location the user stays in that location forseveral hours, a cell phone can continue and measure signal strengths ata desired location hours after the location was identified to the cellphone as a desired location.

The cell phone will be able to determine that it is still at the desiredlocation by measuring the rate the measured signal strengths change andthe relations among them. When a user walks or drives the rate a signalstrength of a specific cell changes will be faster than if the userstayed in one place. The relations between the signal strengths ofsurrounding cells will also change when the user walks or drives awayfrom the desired location. The above therefore enable a cell phone togather more measurements at the desired location at different points intime without requiring the user to identify a place as a desiredlocation more than once.

The suggested method will also be able to recognize changes in thecellular network such as the addition of a new cell or the cancellationof a cell or a retune of the network since the changes will mainly bereflected in one or two measured cells' signal strengths or therelations of one or two measured signal strengths to the strongestmeasured signal etc.

It should be noted that depending on the desired accuracy, the rangefrom the desired location that within the location pending service willstill be activated and so forth, different formulas and methods otherthan the described above might be devised to do the comparison betweenthe measured signal strengths as measured by the cell phone fromsurrounding cells at the current location and desired location.

While the preferred embodiment refers to signal strengths that any cellphone can measure today, cellular networks might decide to use thedescribed invention by using other parameters that they will makeavailable to cell phones.

Such parameters could be for example as follows—a cellular network willbroadcast from all base stations a signal which will be synchronizedamong the base stations (the base stations could be synchronized usingGPS signals). A cell phone will measure the time the same signal willarrive from surrounding cells at a current location. The differentarrival times of the same signal will reflect the distance of the cellphone to the surrounding cells. Those arrival times could be recorded bythe cell phone as the coordinates of a desired location.

The same way, the cell phone recorded, measured and compared signalstrengths from surrounding cells, the cell phone will record, measureand compare the arrival times from surrounding cells of the synchronizedsignal.

Alternatively, a cellular network may decide to send the samesynchronized signal from all base stations and the cell phone willmeasure the phase the signals will arrive to the cell phone with fromthe surrounding cells and the combination of signal phases will be usedas coordinates of locations.

The same way, the cell phone recorded, measured and compared signalstrengths from surrounding cells, the cell phone will record, measureand compare the phases of arriving signals from surrounding cells of thesynchronized signal.

It should be noted that these are just examples, the cellular networksmay decide to make another parameter or combination of parametersavailable to cell phones and the cell phones could use the combinationof measured parameters from surrounding cells as coordinates of alocation.

While the above embodiments describe the usage of the invention for cellphones, the invention can clearly be used in other embodiments where awireless phone can choose between several networks to connect to, whichmeans that the wireless phone can measure the signal strengths ofseveral surrounding networks (or other parameters made available by thenetworks to the wireless phone).

An example of the above will be WiFi hot spots where a wireless phonecan choose between connecting to any of several surrounding WiFi hotspots. The wireless phone could measure the signal strengths of thesurrounding WiFi networks and use the recorded signal strengths as aunique fingerprint of its location.

Another example will be a phone that combines WiFi and cellular byrouting a call over a WiFi network or a cellular network. Such a phonecan measure not only the signal strengths of the surrounding cells butalso the signal strengths of surrounding WiFi networks where thecombined measurements of surrounding WiFi networks and cells willpossibly provide a more accurate location representation. Obviously, theformula used by the phone to combine the measurements of the WiFinetworks signal strengths and the cells signal strengths could varybased on the desired accuracy, used cellular communication protocols(GSM or CDMA or other) etc, A further example, WiMax networks where awireless phone can choose between connecting to any of severalsurrounding WiMax networks. The wireless phone could measure the signalstrengths of the surrounding WiMax networks and use the recorded signalstrengths as a unique fingerprint of its location.

The invention could also be implemented in a phone combiningmeasurements of signal strengths (or other parameters made available bynetworks) from several different networks including cellular networks,WiFi networks and WiMax networks.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the Signal-Comparison Based Location-DeterminingMethod, described systems, and techniques that fall within the spiritand scope of the invention as set forth in the appended claims. Bynon-limiting example, we mention that for purposes of establishing alocation fingerprint (coordinate reference) today's cellular telephonein juxtaposition to established local area base station service antennasis substantially equivalent to a RF communications enabled ubiquitouscomputer in communications with fixed respective base stations antennas;or the likes. Hence, the references to a cellular telephone in thepreferred embodiment may be easily extended to any device capable ofreceiving and measuring a plurality of EMF signals—and therewith tocomply with the other aspects to the instant invention.

While privacy wise, it is preferable to measure signals, record, them,and compare them—all respectively on a portable device per se, there aremany cultures that are less concerned with personal privacy issues. Insuch circumstances, any or all of the steps may be performed from theperspective of service area antenna(s) coordinated by servercommunications there between. The real distinction is that the instantinvention embodiments determine that one is at a specific location froma comparison of signal strengths or like characteristics made at thesame location.

In addition, the instant invention relates to embodiments (and MutatisMutandis to all of the aforementioned instant invention embodimentvariations thereof) of A Signal-Comparison Based Location-DeterminingMethod, operable by at least one portable RF communications device inconjunction with at least two fixed-location service-area antennastations respectively capable of RF communication with the at least onedevice wherein the stations are substantially continuously operating,and the method is comprising the steps of:

-   (A) First-Causing a portable RF communications device at a selected    location to receive an RF communications signal from a plurality of    local fixed-location GSM service-area antenna stations;-   (B) First-Measuring reception signal strength respectively    associated with the “First-Causing” received signal from at least    two of the plurality of antenna stations;-   (C) Second-Causing a portable RF communications device to receive an    RF communications signal from a plurality of local fixed-location    GSM service-area antenna stations;-   (D) Second-Measuring reception signal strength respectively    associated with the “Second-Causing” received signals; and-   (E) Determining, if the portable RF communications device of the    “Second-Causing” step is at the selected location of the    “First-Causing” step, By electronically Comparing at least two of    the respective reception signal measurements of the    “First-Measuring” step with at least two of the respective reception    signal measurements of the “Second-Measuring” step.

Furthermore, the instant invention also relates to embodiments (andMutatis Mutandis to all of the aforementioned instant inventionembodiment variations thereof) of A Signal-Comparison BasedLocation-Determining Method, operable by at least one portable RFcommunications device in conjunction with at least two fixed-locationservice-area antenna stations respectively capable of RF communicationwith the at least one device wherein the stations are substantiallycontinuously operating, and the method is comprising the steps of:

-   (A) First-Causing a portable RF communications device at a selected    location to receive an RF communications signal from a plurality of    local fixed-location CDMA service-area antenna stations;-   (B) First-Measuring reception signal strength respectively    associated with the “First-Causing” received signal from at least    two of the plurality of antenna stations and therewith calculating    respectively relative signal reception strengths;-   (C) Second-Causing a portable RF communications device to receive an    RF communications signal from a plurality of local fixed-location    CDMA service-area antenna stations;-   (D) Second-Measuring reception signal strength respectively    associated with the “Second-Causing” received signals and therewith    calculating respectively relative signal reception strengths; and-   (E) Determining, if the portable RF communications device of the    “Second-Causing” step is at the selected location of the    “First-Causing” step, By electronically Comparing at least one of    the calculated respective relative reception signal strengths of the    “First-Measuring” step with at least one of the calculated    respective relative reception signal strengths of the    “Second-Measuring” step.

Likewise, Mutatis Mutandis to all of the aforementioned instantinvention embodiments and variations thereof, determinations that arebased on derivatives, integrals, statistical metrics, mathematicalnormalizations, correlation functions, heuristic convolution functions,or the likes—are substantially consistent with the “pith and marrow” ofthe instant invention—because the embodiments of the instant inventionare designated for the purpose of knowing a geographical location bycomparing a previously known antenna space measurement (at location “1”)with a current antenna space measurement (performed at location “2”),and deciding if the location of the current measurement (“2”) is to beconsidered as being within a nominal distance from the known measurement(at “1”). Simply stated, the instant invention is verifying that aportable RF reception device is at a geographical location—if itreasonably corresponds to a known antenna space measurement for thatlocation.

In describing the present invention, explanations are presented in lightof currently accepted telecommunications theories and communicationsenabled ubiquitous computing models. Such theories and models aresubject to changes, both adiabatic and radical. Often these changesoccur because representations for fundamental component elements areinnovated, because new transformations between these elements areconceived, or because new interpretations arise for these elements orfor their transformations. Therefore, it is important to note that thepresent invention relates to specific technological actualization inembodiments. Accordingly, theory or model dependent explanations herein,related to these embodiments, are presented for the purpose of teaching,the current man of the art how these embodiments may be substantiallyrealized in practice. Alternative or equivalent explanations for theseembodiments may neither deny nor alter their realization.

Furthermore, numbers, alphabetic characters, and roman symbols asdesignated herein are for convenience of explanations only, and shouldby no means be regarded as imposing particular order on any methodsteps.

Industrial Applicability

Technical Issues: For mobile telephone devices, an ability to measuresignal strength of signals received from local service area antennas andan ability to extract respective ID data from such signals is aself-evident feature. Furthermore, the mobile telephone device generallyhas a reasonable amount of spare computing power onboard. Thus, for themobile telephone device and for many other RF enabled communicationreception with computing capability devices, the method of the presentinvention is straightforward to configure using existing off-the-shelftechnological components.

Ergonomic Issues: The present method allows for user privacy by choice;a feature that is not available at a comparable cost—since a cell phonewith a GPS costs more than a cell phone without a GPS.

Economic Issues: The present method can be implemented on any cheap cellphone which does not include a GPS, thereby bringing location basedservices to the masses by reducing the price of the location determiningmethod used by the phone. Furthermore, the present method facilitatesemergency location reporting in many places where GPS fails; a featurethat can not be expressed in finite monetary terms.

1. A signal-comparison based location-determining method, operable by afirst portable RF communications device in conjunction with a pluralityof fixed-location service-area antenna stations capable of RFcommunication with the first portable RF communications device whereinthe antenna stations are substantially continuously operating, themethod comprising: (a) the first portable RF communications devicemonitoring its location by (i) receiving communications signals from afirst plurality of the antenna stations, (ii) identifying at least oneID within at least one of the received communications signals, and (iii)measuring the signal strengths associated with a received communicationssignal from the first plurality of antenna stations; and (b) the firstportable RF communication device determining if a monitored location iswithin proximity of a location chosen by a user of the first portable RFcommunication device, as a result of (i) electronically comparing the atleast one ID and at least one figure based on the signal strengths ofthe first plurality of antenna stations at the monitored location withthe at least one ID and the at least one figure based on signalstrengths of the first plurality of antenna stations at the locationchosen by the user, and (ii) determining if the difference between thesignal strengths measured at the monitored location and the signalstrengths at the location chosen by the user is less than apredetermined threshold.
 2. The method of claim 1 wherein the chosenlocation signal strengths were measured by the first portable RFcommunication device.
 3. The method of claim 1 wherein the chosenlocation signal strengths were measured by a second portable RFcommunication device, different from the first portable RF communicationdevice.
 4. The method of claim 1 wherein the chosen location signalstrengths and at least one ID originated from a database of geographiclocations and corresponding signal strengths and IDs.
 5. The method ofclaim 4 wherein the database is stored remotely, and not on the firstportable RF communication device.
 6. The method of claim 5 wherein thedatabase is built by a service provider.
 7. The method of claim 4wherein the database is built based on multiple locations, where foreach location, GPS measurements and signal strength measurements areperformed and the IDs of nearby antenna stations of the plurality ofantenna stations are recognized.
 8. The method of claim 7 wherein atleast for some of the locations, signal strength measurements are takenat different times.
 9. The method of claim 7 wherein the signal strengthmeasurements are taken using a portable RF communication device.
 10. Themethod of claim 9 wherein the signal strength measurements orcalculation results made using the signal strength measurements, alongwith the antenna station IDs, are sent by the portable RF communicationdevice to a server responsible for building the database of geographiclocations and corresponding signal strengths and antenna stations IDs.11. The method of claim 4 wherein the chosen location signal strengthsand at least one ID is taken from the database of geographic locationsand corresponding signal strengths and IDs using a geographic locationentered by the first portable RF communication device user as thelocation chosen by the user.
 12. The method of claim 4 wherein thechosen location signal strengths and at least one ID, which correspondswith a geographical location chosen by the first portable RFcommunication device user, is the result of extrapolating the signalstrengths of locations in the database of geographic locations andcorresponding signal strengths and IDs.
 13. The method of claim 4wherein the chosen location signal strengths and at least one ID, whichcorresponds with a geographical location chosen by the first portable RFcommunication device user, is taken from the database of geographiclocations and corresponding signal strengths and IDs, said databasebeing built using computational closure.
 14. The method of claim 1wherein the at least one ID is a cell ID.
 15. The method of claim 1wherein the first portable RF communication device is a mobile phone.16. The method of claim 1 wherein the first portable RF communicationdevice is a ubiquitous computer.
 17. The method of claim 1 wherein themonitoring step comprises ‘low accuracy monitoring’ and ‘high accuracymonitoring’.
 18. The method of claim 17 wherein ‘low accuracymonitoring’ includes comparing the chosen location IDs with the currentlocation IDs.
 19. The method of claim 18 wherein ‘high accuracymonitoring’ takes place only if the current location IDs are determinedto match the chosen location IDs in the ‘low accuracy monitoring’ step.20. The method of claim 19 wherein ‘high accuracy monitoring’ includesmeasuring a signal strength at the current location.
 21. The method ofclaim 1 wherein the monitoring step is performed iteratively, with apredetermined time delay between successive iterations such that datafrom the monitoring step is used only if a substantial portion of thesuccessive measurements are alike within a predetermined threshold. 22.The method of claim 1 wherein the ‘at least one figure based on thesignal strengths’ is the signal strengths, for both the monitoredlocation and the chosen location.
 23. The method of claim 1 wherein the‘at least one figure based on the signal strengths of the firstplurality of antenna stations’ is a figure based on a calculation usingthe signal strengths of the first plurality of antenna stations.
 24. Themethod of claim 1 wherein determining if the monitored location iswithin proximity of a location chosen by the user of the first portableRF communication device further includes informing a location-basedsoftware program application running on the portable device that thedevice is at the location chosen by the user or is no longer at thelocation chosen by the user.
 25. The method of claim 1 whereindetermining if the monitored location is within proximity of a locationchosen by the user of the first portable RF communication device furtherincludes launching a location-based software program application on theportable device when the device is at the location chosen by the user.26. The method of claim 1 wherein the determining of part (b) startstaking place or stops taking place at one or more of the following: (i)at specific time intervals, or (ii) at specific times, or (iii)depending on the rate the user's location changes, or (iv) at theoccurrence of an event, or (v) upon a request from the network, or (vi)upon a request from a software application on the device, or (vii) upona request from the user.
 27. The method of claim 26 wherein thedetermining of part (b) starts taking place or stops taking place at theoccurrence of an event, and wherein the event is the device switchingfrom one to another of the antenna stations with which it is registered.28. The method of claim 27 wherein the antenna station with which thedevice is registered is a cell base station.
 29. The method of claim 27wherein the antenna station with which the device is registered is aWiFi base station.
 30. The method of claim 1 wherein the at least one IDis a WiFi network ID.
 31. A signal-comparison based location-determiningsystem, comprising: (a) a first portable RF communications devicecommunicating with a plurality of fixed-location service-area antennastations capable of RF communication with the first portable RFcommunications device, wherein the antenna stations are substantiallycontinuously operating; (b) software residing on the first portable RFcommunications device, said software causing the first portable RFcommunications device to monitor its location by (i) receivingcommunications signals from a first plurality of the antenna stations,(ii) identifying at least one ID within at least one of the receivedcommunications signals, and (iii) measuring signal strengths associatedwith a received communications signal from the first plurality ofantenna stations; and (c) software residing on the first portable RFcommunication device, said software causing the first portable RFcommunication device to determine if the monitored location is withinproximity of a location chosen by a user of the first portable RFcommunication device, as a result of (i) electronically comparing the atleast one ID and at least one figure based on the signal strengths ofthe first plurality of antenna stations at the monitored location withthe at least one ID and at least one figure based on signal strengths ofthe first plurality of antenna stations at the location chosen by theuser, and (ii) determining if the difference between the signalstrengths measured at the monitored location and the signal strengths atthe location chosen by the user is less than a predetermined threshold.